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Significant and Subsequent Events - Pioneer Pipeline and Skookumchuck Wind Project (Details) $ in Millions, $ in Millions |  |  |  |  | 12 Months Ended |  |
--- | --- | --- | --- | --- | --- | --- | ---
Nov. 25, 2020 CAD ($) MW | Nov. 25, 2020 USD ($) | Oct. 01, 2020 CAD ($) | Apr. 12, 2019 | Dec. 17, 2018 MMcf | Dec. 31, 2020 CAD ($) J | Dec. 31, 2020 terajoule | Nov. 01, 2019 MMcf
Investment [Line Items] |  |  |  |  |  |  |  |
Long-term firm natural gas delivery transportation, amount transferred per day |  |  |  |  |  | 400 | 400 |
SP Skookumchuck Investment, LLC |  |  |  |  |  |  |  |
Investment [Line Items] |  |  |  |  |  |  |  |
Other cash payments to acquire interests in joint ventures, classified as investing activities |  |  |  |  |  | $ 86 |  |
NOVA Gas Transmission Ltd. |  |  |  |  |  |  |  |
Investment [Line Items] |  |  |  |  |  |  |  |
Long-term firm natural gas delivery transportation, amount transferred per day |  |  |  |  |  | 351 | 275 |
Tidewater |  |  |  |  |  |  |  |
Investment [Line Items] |  |  |  |  |  |  |  |
Long-term firm natural gas delivery transportation, amount transferred per day |  |  |  |  |  | 139 | 139 |
Pioneer Pipeline |  |  |  |  |  |  |  |
Investment [Line Items] |  |  |  |  |  |  |  |
Future option to acquire pipeline, ownership percentage |  |  |  |  | 50.00% |  |  |
Pioneer Pipeline | Tidewater |  |  |  |  |  |  |  |
Investment [Line Items] |  |  |  |  |  |  |  |
Proportion of ownership interest in joint operation |  |  |  |  | 50.00% |  |  |
Take or pay agreement, term |  |  |  |  |  | 15 years |  |
Natural gas pipeline capacity (mmcf) | MMcf |  |  |  |  | 50 |  |  | 130
Payments for development project expenditure |  |  |  |  |  | $ 83 |  |
Pioneer Pipeline | Tidewater | Discontinued operations |  |  |  |  |  |  |  |
Investment [Line Items] |  |  |  |  |  |  |  |
Proceeds from sale of assets held for sale |  |  | $ 255 |  |  |  |  |
Skookumchuck |  |  |  |  |  |  |  |
Investment [Line Items] |  |  |  |  |  |  |  |
Proportion of ownership interest in joint operation | 49.00% | 49.00% |  | 49.00% |  |  |  |
Other cash payments to acquire interests in joint ventures, classified as investing activities | $ 86 | $ 66 |  |  |  |  |  |
Capacity of facility (in megawatts) | MW | 136.8 |  |  |  |  |  |  |
Investments in joint ventures | $ 163 |  |  |  |  |  |  |
Value of equity consideration received | $ 77 | $ 59 |  |  |  |  |  |

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